Geomagnetic survey and geomagnetic model research in China

Abstract

The geomagnetic survey at 135 stations in China were carried out in 2003. These stations are with better environmental condition and small magnetic field gradient (<5 nT/m). In the field survey, the geomagnetic declination D, the inclination I and the total intensity F were measured. Ashtech ProMark2 differential GPS (Global Positioning System) was used in measuring the azimuth, the longitude, the latitude and the elevation at these stations. The accuracy of the azimuth is 0.1 . The geomagnetic survey data were reduced using the data at geomagnetic observatories in China. The mean standard deviations of the geomagnetic reduced values are: <1.5 nT for F, <0.5 for D and I . Using the geomagnetic data which include the data at 135 stations and 35 observatories in China, and the data at 38 IGRF (International Geomagnetic Reference Field) calculation points in China's adjacent regions, the Taylor polynomial model and the spherical cap harmonic model were calculated for the geomagnetic field in China. The truncation order of the Taylor polynomial model is 5, and its original point is at 36.0• N and 104.5• E. Based on the geomagnetic anomalous values and using the method of spherical cap harmonic (SCH) analysis , the SCH model of the geomagnetic anomalous field was derived. In the SCH model, the pole of the spherical cap is at 36.0• N and 104.5• E, and the half-angle is 30• , the truncation order K = 8 is determined according to the mean square deviation between the model calculation value and the observation value, the AIC (Akaike Information Criterion) and the distribution of geomagnetic field.

Application of GPS in geomagnetic survey

“…The results for various K (1∼12) were analyzed and compared, K = 5 was finally determined for the Taylor polynomial model. Similarly, for the spherical cap harmonic model, K was respectively taken as 1∼12 during the model calculation; then the results for various K (1∼12) were analyzed and compared, K = 8 was finally determined (Gu et al, , 2006. The Taylor polynomial model of geomagnetic field is convenient in calculation and application.…”

“…In calculating the geomagnetic field model, the results appear larger misfit of ge- omagnetic anomalies in the boundary area when only using the geomagnetic data at 135 stations and 35 observatories in China. After adding the calculation values at some IGRF points in the boundary area, the above-mentioned misfit of geomagnetic anomalies is improved (Gu et al, , 2006Gao et al, 2005). In order to search for the rationality of the number of the added IGRF points and the distribution, a model calculation was done for some groups of selecting 28∼48 IGRF points and the homogeneous distribution.…”

“…2). The Taylor polynomial model and the spherical cap harmonic model (Haines, 1985;An, 2003;Gu et al, , 2006Gao et al, 2005) of geomagnetic declination in China were established. In calculating the geomagnetic field model, the results appear larger misfit of ge- omagnetic anomalies in the boundary area when only using the geomagnetic data at 135 stations and 35 observatories in China.…”

Empirical evidence for latitude dependence and asymmetry of geomagnetic spatial variation in mainland China

“…The research on spatiotemporal geomagnetic variations is routinely carried out in a variety of fields. Different models have been presented to explain the observed trend and variation of the geomagnetic field over small regions, in order to make accurate predictions or to describe the variations of the geomagnetic field over a local portion of the Earth's surface, using Taylor expansions or spherical cap harmonic analyses [ Schott and Thébault , ; Pavón‐Carrasco et al , ; Gu et al , ].…”

“…The research on spatiotemporal geomagnetic variations is routinely carried out in a variety of fields. Different models have been presented to explain the observed trend and variation of the geomagnetic field over small regions, in order to make accurate predictions or to describe the variations of the geomagnetic field over a local portion of the Earth's surface, using Taylor expansions or spherical cap harmonic analyses [Schott and Thébault, 2011;Pavón-Carrasco et al, 2010;Gu et al, 2006]. Some researchers have focused their attention on the large-scale properties of spatial geomagnetic variations [Welker, 2012;Watermann et al, 2006], especially the latitude dependence effect of the geomagnetic field, which has been widely studied via quantitative relations during geomagnetic storms [Ochabová, 1989], the main impulse of geomagnetic sudden commencements [Shinbori et al, 2012] and the westward drift in the main field [Wei and Xu, 2002].…”